Angry Birds: Aspiring to be like Mickey and Mario

FORTUNE — Rovio Entertainment hasn’t made a wrong move yet with its massively popular Angry Birds franchise. The enraged avian creatures are everywhere, picking up wads of cash in their beaks. The original mobile game is still wildly popular, and now there are plush toys on the market and movie and TV deals in the works. The birds are even getting endorsement deals, such as their appearance in a hilarious TV spot for Google’s GOOG Chrome browser.

The “insanely profitable” company is thinking about going public next year, Rovio’s marketing chief, Peter Vesterbacka (a.k.a Mighty Eagle), told Bloomberg Television. But however popular the Angry Birds franchise is now, and however smartly the Finnish company is going about marketing it, there’s no guarantee that the fame will last. People might get sick of the birds. Before it goes public, Rovio probably needs at least one more hit — one that is at most only tangentially related to Angry Birds. Permanent franchises are rarely built on one character alone.

“Disney started as a black and white cartoon about this little mouse,” Vesterbacka told Bloomberg. “Nintendo has been working on Mario for 26 years. Angry Birds is less than two years old.” True, but neither of those cases is really similar to Rovio’s. Disney DIS had Mickey, but then it had Snow White, Pinocchio, Dumbo, Bambi and on and on from there. It created a mouse, but that mouse simply opened the gates. He led Disney into the first full-length animated feature, Snow White and the Seven Dwarves (which had nothing to do with Mickey) and on into television, theme parks and the rest.

Nintendo was a greeting-card and toy company for decades before Mario Bros. It was even a big player in arcade games and home consoles the ’70s, years before Mario picked up his first giant hammer. And anyway, Nintendo was and is a platform — or rather, a set of platforms – on which one can play many games. Like Mickey, Mario merely opened the door, he wasn’t the whole franchise. People might buy a Nintendo console to play Mario Bros., but few would buy one of that was all they could do with it.

For now, though, things are looking great for Rovio. Vesterbacka told Bloomberg that the company is worth “a bit north of” the $1 billion Bloomberg estimates. Besides the aforementioned do-dads, it sells Angry Birds t-shirts, costumes, and even a cookbook. Merchandise reportedly makes up 10% to 20% of revenues. The game is available on all the major mobile platforms, set-top boxes and game consoles. Rovio has begun making inroads to social media, including a Facebook app.

There’s no question that Angry Birds can be Rovio’s Mickey Mouse — the company’s central symbol. But if it wants to entrench itself as a permanent entertainment fixture, Rovio will have to bet the company on something more than a single set of characters. Remember the Cabbage Patch Kids?